1. Field of the Invention
The present invention relates in general to automotive headlights, and more particularly to automotive headlights of a so-called "projector type" which comprises an electric bulb for generating light, a concave reflector for reflecting the light forward, a shade placed in front of the concave reflector for partially shading and thus contouring the reflected light, and a converging lens placed in front of the shade for projecting the contoured light beam forward.
2. Description of the Prior Art
In order to clarify the task of the present invention, one of conventional projector type headlights will be described with reference to FIGS. 14 and 15.
FIG. 14 shows schematically the conventional headlight which is generally designated by reference "a". This headlight "a" is used as a lower beam projector of automobiles. As is known, the lower beam is the light beam intended for a forward neighbouring illumination particularly used when the vehicle is meeting or following other vehicles.
Designated by "b" is a concave light reflector which has an ellipsoidal light reflecting surface "c" formed on an inside face thereof. A light source "d" (viz., a filament of an electric bulb) is placed on a first focus F.sub.1 of the reflecting surface "c" of the reflector "b". A lower half of the light source "d" is concealed by a cap "e", so that the light rays emitted from the light source "d" do not travel to a lower half section of the reflecting surface "c". That is, only the light rays emitted upward from the light source "d" are reflected forward by the upper half section of the reflecting surface "c" and converged at a second focus F.sub.2 of the reflecting surface "c". A shade plate "f" is arranged near the second focus F.sub.2 in such a position that a stepped upper edge "g" thereof is positioned just behind the second focus F.sub.2. A converging lens "h" is arranged in front of the shade plate "f" in such a position that a focus F.sub.c of the lens "h" is placed on the stepped upper edge "g" of the shade plate "f". The reflector"b" and the converging lens "h" are coaxially arranged. The line denoted by "Xl-Xm" is the common axis of these two members "b" and "h".
When, with the arrangement as described hereinabove, the light source "d" is energized to light, the light rays "i" emitted therefrom are reflected forward by the upper half section of the concave reflector "b" and converged at the second focus F.sub.2 of the reflector "b". Due to presence of the stepped upper edge "g" of the shade plate "f" near the second focus F.sub.2, part of the reflected light rays "i" from the reflector "b" is shaded. Accordingly, the light beam projected forward from the lens "h" has such a contoured cross-sectional pattern "j" as shown in FIG. 15. That is, the projected beam from the lens "h" has an inverted image of the upper edge portion of the shade plate "f". The bent line "k" in the pattern "j" in FIG. 15 is provided by the stepped upper edge of the shade plate "f".
However, due to its inherency in construction, the above-mentioned conventional headlight "a" has such a drawback that the projected beam pattern "j" has a specially colored (viz., blue colored) zone "1" along the bent line "k".
That is, since, in the conventional headlight "a", the light rays from the reflector "b" are permitted to go through only the lower half of the lens "h", the light refracting property (viz., spectral characteristic) of only the lower half of the lens "h" works, so that color cancelling effect on the visible spectrum by the lens "h" is substantially lost or at least lowered causing the blue light "i.sub.B " undergoing the greatest amount of deflection to stand out clearly near the axis "Xl-Xm". This phenomenon causes the zone "1" of the projected pattern "j" to be illuminated in blue.